Conventionally, a variable spring constant magnetic spring device, wherein the spring constant can be changed freely, has been proposed as a magnetic spring device of this type. This variable spring constant magnetic spring device is used, for example, as a shock absorbing device for preventing damage to components, attached between a work piece (or a hand) and the tip end of a robotic arm that performs assembly of precision components or small components, such as electronic components.
In assembly by robot, gentle forces are necessary when positioning components because the application of an excessively large contact force would break the component, and after the position has been determined, it is then necessary to press more forcefully. Because of this, a weak force setting, for when performing positioning, and a strong force setting, for after the positioning has been completed, are switched between by the variable spring constant magnetic spring device. Furthermore, it is often necessary to change characteristics of a spring, such as the spring constant or the spring force, such as when a single robotic arm is used for a variety of different jobs, or when changing specifications after installation.
For example, Japanese Unexamined Patent Application Publication No. 2004-360747 shows a conventional variable spring constant magnetic spring device in FIG. 20. This variable spring constant magnetic spring device 400 is structured from a movable element 21 (a movable element yoke 22 and a permanent magnet 23) and a stationary element 24 (coils 25 and 26, gap adjusting stationary yokes 27-30, and stationary cores 31 and 32), a case 33 that supports the movable element 21, and gap adjusting mechanisms 34-37 for changing the spacing of the gap between the movable element 21 and the stationary element 24.
In this variable spring constant magnetic spring device 400, when there is no electric current flowing in the coils 25 and 26, then the magnetic fluxes 40 and 41 from the permanent magnet 23 flow through the yokes 27-30 of the stationary element 24, and the movable element 21 is in a stable state at displacement 0. Because of this, an attractive force is produced that tends to return the movable element 21 to the center point (the origin) of displacement 0, regardless of whether the movable element 21 has a positive displacement or whether it has a negative displacement. Given this, a spring force (a magnetic spring force) is produced in relation to the linear movement of the movable element 21 in a linear direction through the attractive force of the permanent magnet 23 alone.
In contrast, when an electric current is present in the coils 25 and 26, magnetic fluxes 38 and 39 are produced by the coil currents. The magnetic fluxes 40 and 41 by the permanent magnet 23 are weakened by the magnetic fluxes 38 and 39 produced by the coil currents, reducing the magnetic attractive force, thereby reducing the spring constant. Conversely, strengthening the magnetic fluxes 40 and 41 of the permanent magnet 23 through the magnetic fluxes 38 and 39 produced by the coil currents will increase the magnetic attractive force, increasing the spring constant.
Moreover, increasing the spacing of the gaps between the movable element 21 and the stationary element 24 (between 21 and 27, between 21 and 28, between 21 and 29, and between 21 and 30) through the gap adjusting mechanisms 34-37 increases the magnetic resistance, thereby reducing the magnetic attractive force through reducing the magnetic flux that flows through the yokes 27-30 of the stationary element 24 from the permanent magnet 23, reducing the spring constant. Conversely, decreasing the spacing of the gaps between the movable element 21 and the stationary element 24 (between 21 and 27, between 21 and 28, between 21 and 29, and between 21 and 30) decreases the magnetic resistance, thereby increasing the magnetic attractive force through increasing the magnetic flux that flows through the yokes 27-30 of the stationary element 24 from the permanent magnet 23, increasing the spring constant.
However, although, with the conventional variable spring constant magnetic spring device 400 it is possible to vary the spring constant through applying electric currents to the coils 25 and 26, there is the need for continuous consumption of electric power in order to have the magnetic fluxes from the coils act on the magnetic flux from the permanent magnet. This increases the power consumption. Moreover, the greater the power consumed, the greater the heat produced as well, which causes variability in the magnetic characteristics, which is problematic in that this causes difficulties in control.
The present invention was created in order to solve the issues set forth above, and an aspect thereof is to provide a magnetic spring device wherein an arbitrary change in spring characteristics can be maintained without producing the need to continuously consume electric power.